Fixes #24158
Re-lands #24173

This reverts commit 97e03104.

Landing on red to hopefully make less red on the board.

TBR=@goderbauer

Fixes #24158

* Include framework version in JSON output and adds test

This adds flutter create --sample which allows users to execute a command which will create a working sample app from samples embedded in the API docs.

The command looks something like this:

flutter create --sample=chip.DeletableChipAttributes.onDeleted mysample

Fixes #21825

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

When switching between channels, we were leaving around the version freshness stamp file (bin/cache/flutter_version_check.stamp), which meant that the flutter tool would read from that file to see what the cached date of the most recent commit to the current channel (branch) was. The problem was that since the file was created while on the previous channel, the cached date was for the wrong channel, so if you switch from master to beta, flutter would think that the channel was out of date, and a new version was available, at least for three days after the first time it checked (after three days since the last time the freshness was checked, the cached date would get updated).

This PR modifies the channel command to remove that stamp file whenever the user switches channels, so that the cached date will be from the right channel when it is recreated.

Fixes #21134

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

* Remove uses of deprecated constants
* Change int.parse to int.tryParse where appropriate

This reverts commit cc1cf13e.

* adjust declared types to work with dart 2 typing at runtime

* review comments

* update packages/flutter_tools/lib/src/ios/simulators.dart

* Improve update checking

This change emables pinging the server to check for updates regardless of whether the local version is "out of date". The server code already has a 7-day cache so the result is that we can now ping the server once every 7 days instead of waiting for the local install to be 4 weeks out of date before pinging.

The original 4 week period is still used for when we'll start warning the user they're out of date if we could not confirm with the server whether there's a new version.

* Improve message when we know there's a new version available

* Fix bnullable bool checks

* Switch nullable bool to enum

* Fix casing of enum values

* Remove stale comment

The names are now descriptive so doesn't need additional explanation.

* Improve name of function

* Remove note:

* Rename kPauseToLetUserReadTheMessage -> timeToPauseToLetUserReadTheMessage

* Change kVersionAgeConsideredUpToDate to 5 weeks from 4

* Inline the isNewerFrameworkVersionAvailable check

* Fix indenting (?)

* Fix more indenting

* Rename function to be clearer it's getting the commit date

* Formating tweaks

* Update stamp when connection failed, and reduce time before we'll try again

Previously we would hit the server on every command if we thought we might be out of date and we never successfully connected (eg. if you're offline). This makes the stamp update even when there's a conneciton failure so that this won't happen, but reduces the time till we check again from 7 days to 3 days to compensate a little in case it was a one-off.

https://github.com/flutter/flutter/pull/18193#issuecomment-399222269

* Fix comment

* Don't perform update checks if not on an official channel

Our style guide says the k's are not necessary, and it seems like a good idea to make all the code be consistent on this.

Only naming changes to private vars: no logic changes.

Revert some uses of Number.tryParse(), ignore deprecation warnings for Number.parse()

* Handle error count reported by frontend.

Extend compilation result from single string to a structure(string filename and integer error count).

* Use ?.

* Include engine roll with dart sdk roll.

* parse(onError) -> tryParse

* Make '?? throw' more readable and avoid issue with analyzer

* Fix test so it mocks compiler output including errors count

This updates AppContext per the recommendations in #15352

Fixes #15352

* Use already downloaded dart sdk for frontend_server.

This is follow-up to https://github.com/flutter/flutter/pull/14610

* Remove reference to engine dart-sdk from artifacts

* Remove unused imports

* WIP to switch back to solution where dart sdk is downloaded into bin/cache/dart-sdk, but it is 'flutter precache -a' that can download all dart sdks for other platforms under bin/cache/artifacts/engine/<platform>/dart-sdk

* Download all dart sdks when 'flutter precache -a'

Fixes https://github.com/flutter/flutter/issues/14232

(I haven't tested this with older versions of git, I'm just going on
what @jason-simmons wrote in the bug.)

Generate the "version" file from git tags.
Remove the old VERSION file and mentions of versions in pubspec.yaml files.
Replace the old update_versions.dart script with a new roll_dev.dart script.
Update "flutter channel".
Update "flutter upgrade", including making it transition from alpha to dev.
Update "flutter --version" and "flutter doctor".

* Add capability to print engine dart sdk to flutter doctor

* First round of review comments

* second round of comments

* Final review comments